This invention relates to a metal case for housing an IC and a manufacturing method therefor, and more particularly, it relates to a thin metal case for housing electronic parts which include IC's and a manufacturing method. Such a metal case can be used for thin products, typical examples of which are card-shaped electronic products such as IC cards and card-type electronic calculators. In the present specification, an explanation will be given with respect to IC cards as a typical example, but the present invention can of course be used for housing any thin, plate-shaped electronic products which contain IC's or other electronic parts.
At the present time in the so-called "card age", as computers develop and become more wide-spread, the use of IC cards which contain integrated circuits which serve as data storage devices and data processing devices is being investigated as a replacement for conventional magnetic cards having magnetic tape bonded thereto. IC cards have a far greater data storage capacity than magnetic cards, and research and development is being carried out concerning their application in various fields, such as in banking where IC cards could be used instead of bankbooks, or in health care where they could be used instead of clinical charts for patients.
As a rule, it is necessary for an IC card to have the same thickness (about 0.7 mm) as conventional magnetic cards, but with an IC card in the form of a plate-shaped plastic base which houses an IC chip, bending produces severed wires where the IC chip is bonded, and there is the possibility of data loss or of the IC card being rendered malfunctional.
The use of an IC card in which the IC chip and other electronic parts are housed in a metal case and the bending stiffness is increased is being studied. Such an IC card has excellent durability when subjected to rubbing or when it becomes dirty. Furthermore, if a material such as stainless steel or titanium is used for the metal case, there is no worry of rusting occurring.
FIG. 1 illustrates two examples of conventional packages for IC cards of this type. FIG. 1a is a cross-sectional view of a package which is formed from a plastic base 1, which supports an IC and other electronic parts, and two metal sheets 2 which are laminated to both sides of the base 1. IG. 1b is a cross-sectional view of an example in which two metal cases 3 which are formed from metal sheets into shallow vessels are bonded to and cover a plastic base 1. In FIG. 1b, on account of the walls 3' of the metal cases 3, the IC card has greater stiffness than the IC card of FIG. 1a. Alternatively, when the two cases have the same stiffness, the thickness of the metal cases 3 is less than that of the metal sheets 2 of FIG. 1a.
As the periphery of the plastic base 1 is also covered by metal sheet, the IC card has excellent durability and reliability, and moreover it is protected against static electricity. An IC card having a metal package of the type shown in FIG. 1b is described in Japanese Published Unexamined Patent Application No. 61-258798.
With a conventional IC card, when attempting to learn what information is stored inside it, it is necessary to go to a bank or other place having a card reader, and therefore it is not possible for the user of the card to easily read the stored information.
Recently, however, displays for displaying the stored information and keyboards for inputting information have been built into IC cards, and research is being performed on IC cards of this type having the same thickness as conventional cards. IC cards of this type contain a larger number of devices than conventional cards and therefore require high rigidity. For such cards, the metal case structure illustrated in FIG. 1b is inadequate.
The stiffness of the metal cases 3 of an IC card having the structure shown in FIG. 1b can be increased without increasing the total thickness by making the walls 3' sturdier. In this case, as shown in FIG. 2, a metal case 4 which has a thickness T and which can house the entirety of a plastic base 1 is employed, and it is covered by a cover 5 made from a metal sheet. It is necessary to make the thickness b of the walls 4' of the metal case 4 sufficiently large.
FIG. 3 shows one example of an IC card using a metal case. FIG. 3a is a plan view, and FIG. 3b is a cross-sectional view. The lengths l.sub.1 and l.sub.2 are the same as for a conventional magnetic card made of plastic. According to international specifications, l.sub.1 =85.60 mm and l.sub.2 =54.00 mm. The corner radius R=3.0 mm, for example. The total thickness T is the same as for a conventional magnetic card, and is 0.76 mm according to international specifications.
An IC chip and other electronic parts are housed inside a space 6 formed by a vessel-shaped metal case 4 and a metal cover 5. The plate-shaped metal lid 5 is connected to the metal case 4 and they together constitute a finished product 7 such as an IC card. The inner space 6 is closed. The metal cover 5 is equipped with a display 8 for the stored information and keys 9 such as a power switch and input buttons. The thickness t.sub.c of the metal cover 5 is about 50 .mu.m. The IC chip and other electronic parts which are housed within the space are prevented from breaking due to bending largely by the metal case 4.
FIG. 4 shows a conventional metal case 4. FIG. 4a is a plan view, and FIG. 4b is a cross-sectional view. As stated previously, the metal case 4 is in the shape of a vessel and has a depression 10 which houses an IC chip and other electronic parts. A rim 4b having the shape of a picture frame is provided around the depression 10. Its widths are b.sub.1 =2 mm and b.sub.2 =3 mm, for example. The lengths l.sub.1, l.sub.2 and the radius R are the same as in FIG. 3.
The thickness t.sub.b of the rim 4b is 0.6.-0.7 mm, while the thickness t.sub.a of the bottom 4a need only be about 0.1 mm. Namely, in spite of having an extremely thin bottom, the metal case 4 has a depression 10 with a large area.